1. Field of the Invention
The present invention relates to methods and apparatus for converting flat boards for use in constructing ducts and duct fittings. The methods and the apparatus are particularly well suited for use with boards that are rigid or semi-rigid and are produced specifically for use in fabricating insulated ducts for heating, ventilating and air conditioning applications.
2. Description of the Prior Art
Boards that are commercially available today are being produced for use in forming thermally insulating ducts such as are employed for heating, ventilation and air conditioning. In one case, these boards consist of a rigid foamed plastics material, namely, a closed cell expanded phenolic foam in the form of a planar board having a metallic foil such as aluminum bonded to each major surface. One example of such a board is sold under the trademark KOOLDUCT®. The apparatus and methods of the present invention are especially well suited for use with such planar boards although the methods and apparatus are also suitable for use with other foil faced planar boards, for example, boards consisting of open cell or closed cell expanded foam materials, such as polyurethanes. Such boards are referred to herein generally as “foam boards”. They are to be distinguished from other duct materials such as sheet metal and fiber board typically made from glass fibers with resins and/or binders to provide stiffness.
The fabrication of ducts and duct fittings from foam boards is quite different from the fabrication of ducts and duct fittings from conventional metal sheets. For one thing, sheet metal can be treated fairly roughly and foam board, in general, tends to be more fragile and frangible than sheet metal and some extra care needs to be taken in handling foam board and in fabricating ducts and duct fittings from it. However, foam board is remarkably light, with excellent thermal insulating properties, and often sufficiently rigid itself for duct applications although long unsupported spans, large cross-sectional areas, or significant differential pressures between interior and exterior may require reinforcement or additional support. There are numerous other advantages to foam board in heating, ventilating and air conditioning applications, vis-à-vis sheet metal and fiber board, as well. Foam board is very robust. Ducts made from it can handle pressures of up to four inches of water column. Accordingly, better fabrication apparatus and methods are needed to expand the use of this important material.